1. Field of the Invention
The present invention relates to the esterification of polysaccharides with a ketene dimer using enzymatic and chemical methods. This invention also relates to novel compositions obtained through lipase-catalyzed xcex2-lactone ring opening alcoholysis of ketene dimers, and to products containing the compositions.
2. Description of Background and Related Art
Esters of polysaccharides such as cellulose ethers are usually prepared by converting polysaccharides to the monoesters by various chemical synthetic methods using carboxyl anhydrides. (C. J. Malta, Anal. Chem., 25(2), 245-249, 1953; C. J. Malta, Industrial and Engineering Chemistry 49(1), 84-88, 1957). Different types of mixed monocarboxyl esters of cellulose and cellulose ethers have been chemically synthesized, such as cellulose acetate succinate (J of Pharm. Sci. 51, 484, 1962) and hydroxypropyl cellulose acetate succinate (EP 0219426, Jun. 10, 1986).
The effect of alkyl ketene dimer (AKD) in sizing paper is disclosed in S. H. Nahm, J. Wood Chem. Technol., 6(1), 89-112, 1986; K. J. Bottorff, Tappi J. 77(4), 105-116, 1994, and Nord. Pulp Pap. Res. J. 8(1), 86-95, 1993. However, ketene dimers have not been used in an enzymatic process to form esters of polysaccharides or polysaccharide derivatives. AKD has also not been used to chemically react with polysaccharide in order to intentionally make such esterified polysaccharide products.
AKDs have an activated lactone functionality that reacts with hydroxyl and amine groups under mild conditions, which avoids the requirement of using an acyl chloride or anhydride. AKD starting materials are cheap and there are few or no by-products after the reaction.
Therefore, it would be advantageous to use ketene dimers as one of the starting materials to make esterified polysaccharides.
The present invention provides a product comprising a novel esterified polysaccharide manufactured using an enzyme as a catalyst under mild reaction conditions with relatively high yields. Specifically, the present invention provides for an esterified polysaccharide product having the general formula:
[Rxe2x80x94O]xe2x80x94COxe2x80x94CH(R1)xe2x80x94COxe2x80x94CH2xe2x80x94R1
wherein R is a polysaccharide, and R1 is a linear or a branched aliphatic or olefinic chain having 2 to 20 carbons; in combination with an enzyme of a type that catalyzes the formation of the esterified polysaccharide. This esterified polysaccharide is a reaction product between a polysaccharide and a ketene dimer. The enzyme maybe in deactivated form by the end of the reaction.
The product has about 80 to 100 wt. % of esterified polysaccharide, based on the total weight of the product and the esterified polysaccharide product contains about 0.10 to 10 wt % of the reacted ketene dimer based on the total weight of the esterified polysaccharide product. The enzyme is obtained from animal, plant, bacteria, virus, yeast, fungi, or mixtures thereof. The enzyme used is preferably a hydrolase. It can preferably be a lipase or a protease. The lipase maybe obtained from a source selected from a group consisting of Pseudomonas sp., or Pseudomonas fluorescens, Candida antarctica, Candida rugosa, Candida cylindracea, Porcine pancreas, Rhizopus delemar, and Rhizopus Niveus. Preferably, the lipase is obtained from Pseudomonas sp. or from Pseudomonas fluorescens. 
The polysaccharide used is at least one selected from the group consisting of cellulose ethers, hydroxyethylcellulose, hydroxypropylcellulose, carboxymethylcellulose, guar, cationic guar, and hydroxypropylguar. Preferably, it is hydroxyethylcellulose with a molar substitution of about 2.0 to 4.0. More preferrably, the molar substitution is about 2.5.
The ketene dimer used is at least one of (A) alkyl ketene dimer (B) alkenyl ketene dimer, and (C) ketene dimer of mixed fatty acids; and the ketene dimer can be grafted onto the polysaccharide during the reaction. The alkyl ketene dimer is one selected from linear or branched aliphatic chains having 8 to 44 total carbons. The alkenyl ketene dimer is preferably one selected from linear or branched alkenyl chains having 8 to 44 total carbons with 0 to 6 total double bonds. The fatty acid of the fatty acid ketene dimer is aliphatic or olefinic with 4 to 22 carbons. Preferrably, the ketene dimer is at least one selected from the group consisting of stearyl, palmityl, oleyl, linoleyl groups and mixtures thereof.
The product of this invention can be water-soluble or water-insoluble. It has a viscosity of about 1 to 300 times higher than that of the polysaccharide before the reaction. Preferably, it has a viscosity of about 20 to 300 times higher than that of the polysaccharide before the reaction. Such higher viscosity remains substantially unchanged after three days at pH of about 6.5 to 8.5. The molecular weight of the product is about 1,000 to 3,000,000.
More specifically, the present invention provides an esterified polysaccharide that is an enzymatic reaction product between a polysaccharide or a polysaccharide ether and a ketene dimer. The polysaccharide ether has a molar substitution of about 0 to 4.0. The ketene dimer is an aliphatyl or olefinyl ketene dimer. The enzyme, which may be a lipase obtained from Pseudomonas sp. or from Pseudomonas fluorescens, is preferably in deactivated form by the end of the reaction. This product preferably has a viscosity about 20 to 300 times more than that of polysaccharide before reaction.
The present invention also provides a process of making an esterified polysaccharide that includes a step of adding an effective amount of enzyme to a polysaccharide reaction mixture. The reaction mixture comprises organic solvents, polysaccharides, and a ketene dimer. The organic solvent medium is at least one selected from the group consisting of hydrocarbons, polar aprotic solvents, and non-polar solvents. The organic solvent medium is preferably a non-polar solvent selected from the group consisting of ketones, ethers, and cyclic ethers. Most preferably, the organic solvent medium is a polar aprotic compound. The polar aprotic compound is at least one selected from the group consisting of N,N-dimethylacetamide, N,N-dimethylformamide, and dimethylsulfoxide. The organic solvent medium is present in an amount of about 10 to 95 wt. % based on the total weight of the reaction mixture. The polysaccharide in this process is present in an amount of about 1 to 75 wt. % based on the total weight of the reaction mixture. The ketene dimer is present in an amount of about 0.10 to 10 wt. % based on the total weight of the reaction mixture. The reaction mixture temperature is maintained at between about 20xc2x0 C. to 100xc2x0 C. during reaction, preferably between about 40xc2x0 C. to 60xc2x0 C. The reaction time is between about 1 to 72 hours, preferably, between about 6 to 24 hours. The process further comprises deactivating the enzyme by the end of the reaction. The process further comprises washing the reaction product with isopropyl alcohol. The process further comprises drying the washed reaction product.
In specific preferred embodiments, the process includes: adding enzyme in the amount of about 0.013 to 13 wt. % based on the weight of polysaccharide to a reaction mixture; wherein the reaction mixture comprises (A) cellulose ether or guar ether; (B) an alkyl or alkenyl ketene dimer; and (C) an organic solvent selected from the group consisting of N,N-dimethylacetamine, N,N-dimethylformamide, and dimethylsulfoxide; heating the reaction mixture for about 6 to 24 hours at about 40xc2x0 C. to 60xc2x0 C.; deactivating enzyme after the completion of the reaction; washing the reaction product with an alcohol such as isopropyl alcohol; and drying the reaction product.
This invention also provides a chemically modified polysaccharide product having the general formula:
[Rxe2x80x94O]xe2x80x94COxe2x80x94CH(R1)xe2x80x94COxe2x80x94CH2xe2x80x94R1
wherein R is a polysaccharide, and R1 is a linear or a branched aliphatic or olefinic chain having 2 to 20 carbons. This chemically modified polysaccharide is also an esterified polysaccharide product.
Specifically, in other preferred embodiments, this invention also provides an esterified polysaccharide product that is a chemical reaction product between a polysaccharide and a ketene dimer. The polysaccharide ether has a molar substitution of about 0 to 4.0. The ketene dimer is an aliphatyl or olefinyl ketene dimer. The esterified polysaccharide has about 80 to 100 wt. % of polysaccharide based on the total weight of esterified polysaccharide. This product preferably has a viscosity about 2 to 1000 times more than that of the polysaccharide before the reaction.
This invention also provides a process of chemically making a modified polysaccharide by reacting polysaccharide with ketene dimer in a reaction mixture. The weight ratio between ketene dimmer to polysaccharide is about 0.0013 to 0.13.
Specifically, in other preferred embodiments, this invention also provides a process of chemically making an esterified polysaccharide product by: heating the reaction mixture for about 4 to 72 hours at a temperature of about 40 to 120xc2x0 C.; wherein the reaction mixture comprises: (A) a hydroxyethyl cellulose; (B) an aliphatyl or olefinyl ketene dimer; and (C) an organic solvent being one of N,N-dimethylacetamine, N,N-dimethylformamide, and dimethylsulfoxide; washing the reaction product with an alcohol such as isopropyl alcohol; and drying the reaction product.
The esterified polysaccharides have many applications. They may be used in paints as thickeners and stabilizers, in construction materials to impart shear or tensile strength, or for personal care applications as polymeric emulsifiers. They may also be used for encapsulation, as excipients for pharmaceutical tablets, and as antihalation coatings. They may also be used as ingredients in detergents.
The present invention also provides a product that comprises a composition of modified ketene dimer having the general formula:
[Rxe2x80x94O]xe2x80x94COxe2x80x94CH(R1)xe2x80x94COxe2x80x94CH2xe2x80x94R1
wherein R is a hydroxyl-containing compound, and R1 is a linear or a branched aliphatic or olefinic chain having 2 to 20 carbons; in combination with an enzyme which can catalyze the formation of the modified ketene dimer.
Specifically, the composition comprises xcex2-lactone ring-opened and alcoholized ketene dimer which is an enzymatic reaction product between a hydroxyl-containing compound and a ketene dimer, in the presence of about 0.13 to 13 wt. % enzyme based on the weight of said hydroxyl-containing compound. The hydroxyl-containing compound is at least one of (A) a polyethylene glycol, (B) ethanol, (C) methanol, and (D) sucrose. The ketene dimer is an aliphatyl or olefinyl ketene dimer. The enzyme is a lipase obtained from Pseudomonas sp. or from Pseudomonas fluorescens. 
This invention also provides a process of making a modified ketene dimer by adding an effective amount of enzyme to a ketene dimer reaction mixture.
Specifically, this invention also provides a process of making a xcex2-lactone ring-opened and alcoholized ketene dimer by: adding enzyme in the amount of about 0.1 to 100 wt. % based on the weight of ketene dimer to a reaction mixture; wherein the reaction mixture comprises (A) one of polyethylene glycol, ethanol, methanol, and sucrose; (B) an alkyl or alkenyl ketene dimer; and (C) an organic solvent of t-butyl methyl ether; heating the reaction mixture for about 24 to 72 hours at about 50xc2x0 C.; deactivating enzyme after the completion of the reaction; and washing the reaction product with hexane.